Irrigation systems are frequently used to deposit water and/or pesticides throughout a field of crops. A typical irrigation system includes multiple spans linked together and moved through the field on frame pieces or “mobile towers” having wheels. A center-pivot irrigation system moves in a circle or semi-circle about a center-pivot while a lateral-move irrigation system moves along a generally straight line across a generally-square or rectangular-shaped field.
Many irrigation systems are designed to automatically adjust the alignment of the spans relative to each other and/or relative to the center-pivot as the spans move across a field. For example, it may be desirable to adjust alignment of one or more spans to relieve stress in the pipe carried by the spans, caused by an uneven grade, or to cause one or more spans to wrap or swing around obstacles in a path of the irrigation system.
Some center-pivot irrigation systems use constant speed motors with on/off duty cycles for movement of mobile towers to adjust span alignment. Alternatively, when constant motion is required, an irrigation system may use variable frequency drives (VFD) or a hydraulic drive pivot to variably speed up or slow down any one of the mobile towers. However, both of these solutions can be expensive and difficult to install.